The invention relates to compensated inhalation-exhalation valves for use in breathing systems, particularly for the crew members of planes operating at high altitude. It more particularly relates to those inhalation/exhalation valves which are carried by a mask within which an overpressure may prevail and whose gas control member includes a deformable diaphragm having a rotational symmetry, with a cup whose bottom wall is formed with a substantially radial lip seal cooperating with an exhalation seat.
Exhalation valves exist which include a deformable diaphragm and are compensated for the overpressures prevailing within the mask and which are necessary for high altitude flights. Compensation is achieved by an appropriate gas pressure acting against the end wall of the cup, in a direction which biases the lip seal onto its seat. That approach has proved satisfactory up to altitudes attained by the present fighter planes. However, the planes now under development are designed for altitudes and accelerations which may exceed the possibilities of the diaphragm. For instance, it is hardly possible to have a compensation pressure over 50 mbars on the cup. And high load factors may result in a deformation of the diaphragm detrimentally affecting its operation.
It is an object of the invention to provide an improved inhalation/exhalation valve for high altitude high acceleration use. It is a more specific object to provide a valve which is reliable in operation and does not exhibit variations under very high overpressures. It is still another object to provide a valve which can operate under high acceleration loads, the latter result being obtained by a reduction of the weight of the movable parts.
An inhalation/exhalation valve according to the invention comprises a deformable diaphragm having a rotational symmetry, comprising a central cup whose bottom is integral with a substantially radial lip seal cooperating with an exhalation seat, said cup being annular and defining a toroidal chamber in which compensation pressure prevails.
For countering deformation of the diaphragm, a rigid stiffening ring is secured to the diaphragm for transmitting forces between the cup and the lip seal. The stiffening ring may be secured to a cylindrical projection which connects the bottom wall of the cup and the lip seal to a part of that lip seal approximately up to a circular line along which the lip seal cooperates with the exhalation seat.
The cup may include a flat portion and two folds whose shape approximates a quarter of a circle in cross-section. The folds have end rims clamped within a housing. The size and shape of the folds may be such that the effective area subjected to compensation pressure on the diaphragm be substantially equal to the area defined by the line of abutment of the lip seal onto the exhalation seal, or slightly higher for obtaining an overcompensation. The rigid stiffening ring secured to the diaphragm and stop means in the housing may be arranged for limiting "bulging" deformation of the cup, which is preferably so constructed that the center of the fold (which approximately corresponds to the limit of the effective area subjected to the compensation pressure) has a radial movement as small as possible upon modification of the compensation pressure. Overcompensation should remain positive, but must be as low as possible within the complete range of compensation pressure. That overcompensation is in addition to the expiratory head losses. According to the invention, the increase of the amount of overcompensation in response to increase of the compensation pressure, which is frequently found in prior art devices, may easily be avoided.
An inhalation valve may be integrated to the diaphragm as a second lip, radially directed opposite to the lip seal cooperating with the exhalation seat. All functions of the valve may then be fulfilled by a single piece, at the cost of a slight increase in the diameter of the diaphragm.
The invention will be better understood from the following description of particular embodiments of the invention, given by way of examples only.